Crown Plastics Case Histories For Material Handling
DuraSurf™ ASC-UV is a black pigment UHMW-PE blend with a 1% carbon content. The carbon gives the plastic the highest level of conductivity in the industry with a surface resistivity of 102-103. The black pigment also provides a high level of UV resistance, lasting up to 10 times longer in the outdoors than other UHMW-PE products.
DuraSurf™ ASC-UV in Conductive Applications
In consumer product manufacturing, conductivity restrictions stipulate that plastics used in special applications or manufacturing environments resist tribocharging and the build-up of common static electricity.
Tribocharging occurs when two dissimilar surfaces come into contact with each other and then separate. The separation causes the release and transfer of electrons from one surface to the other. As electrons accumulate on the surface of the receiving surface, the potential for ESD (electrostatic discharge) increases. The intensity of the static build-up and the strength of any discharge are affected by such variables as the types of materials involved, their surface roughness and temperature, and the amount of humidity in the air.
The discharge, when it occurs, may be visible (spark) or invisible. A discharge in areas that are subject to gas, fuel vapor, or dust accumulation may cause an explosion and fire. A discharge near sensitive electronic devices may cause component failure.
DuraSurf™ ASC-UV, as a conductive plastic, resists electron build-up and the potential for electrostatic discharge. This makes the product suitable for use in clean rooms and in applications involving the assembly of electronic components.
In material handling environments, DuraSurf™ ASC-UV prevents the accumulation of static electricity around moving components and electronic devices. When applied in chute lining applications (with or without additional silicone additive*), the resistance to electron build-up allows lightweight poly bags and shrink-wrapped products to move freely across the chute surface.
DuraSurf™ ASC-UV in UV-Stabile Applications
The combination of black pigment and 1% carbon increases DuraSurf™ ASC-UV’s resistance to UV rays. In outdoor environments where the plastic is subject to only indirect exposure to sunlight, the lifespan of the product is substantial. And even in direct exposure, DuraSurf™ ASC-UV has proven stabile up to ten times longer than similar products.
When combined with an acrylic pressure sensitive adhesive, UV-stabile applications for DuraSurf™ ASC-UV extend to include environments with high heat and moisture. Acrylic adhesive adds moisture resistance and heat tolerance characteristics to product performance. Although not moisture proof, applications that place DuraSurf™ ASC-UV in direct exposure to sun and rain will hold up longer.
Industry Case Study
It’s common practice to use plastics to improve product flow and soften impact in material handling systems. But given the right conditions, these same plastics will also generate static electricity.
One field application study found that a carton passing over a plastic transition plate not only generated static electricity, it would occasionally cause a spark as it crossed from one steel chute to another. In specific cases, these sparks resulted in a fire. Aerosol cans packed in boxes discharged a portion of their contents during shipping and conveyance. The flammable liquid soaked through the cardboard to the outside surface. The spark ignited the liquid and the cardboard, setting fire to the carton, even as it continued to move through the conveyance system.
Fortunately, technicians were able to isolate the source of the spark. The plastic transition plates were replaced with rubber-backed sections of DuraSurf™ STS, a specially formulated DuraSurf™ ASC-UV containing a silicone additive. The rubber backing lessened package impact during transition. The silicone additive further improved product movement between the steel beds. And the 1% carbon (black) component in the ASC-UV / STS material eliminated sparking during transition.
Ease of Application
Crown’s thin-gauge UHMW-PE tapes are manufactured in several standard thicknesses. Tapes are slit to customer width and shipped in 50’ and 100’ rolls. Custom slitting allows the end-user to tailor the finished tape to fit the requirements of the application and the adhesive backing eliminates the need for mechanical fastening. When applied to a properly prepared clean, smooth, flat, dry surface, adhesive-backed tapes will stick to almost any substrate. The available line of pressure sensitive adhesives is intended to fit a variety of situations: indoors and outdoors, high heat and low heat, wet and dry.
The Middle Market
The North American market for UHMW-PE is built largely upon thick sheet and skived film applications. But Crown Plastics manufacturing process is unique. Using an in-line compression molding process, Crown creates sintered UHMW-PE in gauges that both crossover and fit between the skived and sheet categories. The sintering process gives tight thickness control. It also allows for the addition of pigments, UV stabilizers, silicone, carbon and other additives. And fitting between the markets allows Crown to create UHMW-PE products in small and large quantities that are cost and material efficient.
DuraSurf™ ASC-UV tapes are available with pressure sensitive adhesive backing and in wear strip form (no adhesive backing). A wide range of adhesive backings makes DuraSurf™ ASC-UV a practical solution for many ESD- and UV-requirement applications.
- Conforms to ASTM-D-4020
- Flammability rating UL 94 HB
- High abrasion and wear resistance
- High impact strength
- No moisture absorption
- Chemical and corrosion resistant
Standard thickness: .031” (.78mm) – .040” (1.02mm) – .062” (1.57mm) – .080” (2.03mm) – .093” (2.36mm) – .125” (3.17mm)
Thickness tolerance: +/-10%
Available widths (trimmed to customer requirements): 0.25” (6.35mm) to 24” (610mm)
Width tolerance: +/-0.031” (.78mm)
Standard roll lengths: 50’ (15.25m) and 100’ (30.5m)
*Crown Plastics also manufactures DuraSurf™ STS, a conductive and UV-stabile UHMW-PE with a silicone treated surface. DuraSurf™ STS is commonly used in material handling applications.
- Friction – created as the conveyor belt runs on the steel slider bed
- “Reversion Effects” – the build up of dirt and belt fibers on the steel bed resulting in drag between the belt and steel slider bed
- Belt lacing drag and wear on the conveyor bed
- Heavy loads on the belts
- The excessive use of high-horsepower drive motors to compensate for friction, drag, and wear between the belt and steel bed.
Solution: Crown Plastics has found that lining the steel slider bed with DuraSurf ™ STS (Silicone Treated Surface UHMW-PE) with pressure sensitive adhesive backing will reduce the coefficient of friction between the belt and the steel bed and greatly eliminate reversion.
DuraSurf ™ STS
DuraSurf ™ STS UHMW-PE is abrasion resistant and very slick, with a low coefficient of friction. The addition of silicone to the resin blend helps maintain abrasion resistance while enhancing the low coefficient of friction. Heavy products, which normally increase belt contact and slow the system, move freely. Energy requirements are reduced because the plastic allows the conveyor belt to function efficiently. In addition, maintenance costs (to repair/ replace belts and motors) and conveyor system downtime are greatly reduced.
Crown Plastics DuraSurf ™ STS offers the following advantages:
- High abrasion resistance – the highest abrasion resistance of any thermoplastic polymer (5 times greater than stainless steel)
- High impact strength, even at very low temperatures
- Excellent slide properties due to the low coefficient of friction
- Self-lubricating (non-caking and sticking)
- Chemical and stress crack resistance
- Sound dampening properties
- Easy machining – trimming, stamping, cutting, etc.
Conveyor System Energy Savings Test Methods and Results
Assessing current power consumption and the potential for energy savings required testing an existing conveyance system. A power meter was connected to a conveyor belt operating at a normal load cycle. Power readings were recorded for a two-week period.
The data captured for the operating period was evaluated to determine:
- Total energy usage
- Monthly estimated usage
- Peak demand usage
- Peak average usage.
Particular attention was given to peak usage. Peak usage measurements are important because these typically determine the energy rate charged to the consumer.
Strips of adhesive-backed DuraSurf ™ STS UHMW-PE were then applied to the steel slider bed and the experiment was repeated. The DuraSurf ™ STS strips lowered the coefficient of friction between the belt and the bed, reduced the points of contact between the belt and the bed, and provided energy savings.
In fact, when applied to a slider bed conveyor, DuraSurf ™ STS UHMW-PE has been proven to reduce energy consumption by 15% to more than 30% while also eliminating wear on the slider bed and extending the life of the belts and drives.
Installing DuraSurf ™ STS in a Slider Bed Conveyor
A typical installation of DuraSurf ™ STS involves adhering three-inch-wide strips of the material at approximately six-inch intervals (or spaced to evenly distribute the strips across the width of the slider bed).
It is also possible to fully cover the width of the steel bed. But Crown Plastics has found that, with the UHMW’s already low coefficient of friction, interval strips sufficiently reduce the points of contact between the belt and the steel bed and provide the best results.
The following is the recommended procedure for proper installation of DuraSurf ™ STS to a slider bed. NOTE: It is recommended that the temperature be above 50°F (10°C ) when installing material backed with pressure sensitive adhesive.
Installing Crown Plastics DuraSurf™ STS to a Slider Bed
Pressure-sensitive systems work well in a wide variety of applications as long as environmental and substrate conditions are considered.
The following are guidelines for selecting a pressure-sensitive adhesive for an application.
Determine the continuous operating temperature. Anything over 125°F continuous will probably require an acrylic system. While rubber adhesive systems are very versatile and aggressive, this is one area that rubber systems do not do well.
Identify the surface energy of the substrate. It is the surface energy that determines whether a substrate is bondable or not. PTFE and polyethylene have very low surface energies and are difficult to bond. The surface of these materials will need some form of treatment to increase surface energy and enhance bondability.
Consider whether the adhesive is exposed to concentrated solvents. Some adhesive systems are very susceptible to solvent exposure. Exposure can break down the adhesive system. Solvent exposure will require an adhesive with cross-linking to withstand exposure to these chemicals.
Determine if the adhesive is exposed to weathering. Excessive moisture and temperature variations can also wreck havoc on a pressure-sensitive adhesive. Knowing the varying temperature ranges will immediately determine if a rubber or acrylic is best suited. The ability to repel moisture or function in a high moisture environment will also narrow down your adhesive selection.
Determine if the adhesive is exposed to direct UV exposure. Outdoor exposure and UV light will break down a rubber-based system rather quickly. As a rule, acrylic adhesives are recommended for outdoor use. They provide excellent UV stability and temperature performance.
Identify any migrating agents exposed to adhesive. Some substrates may contain plasticizers or agents that may migrate to the surface. These agents may interfere with the adhesive’s ability to latch on to the substrate and delamination may occur. In most cases a cross-linked acrylic will function well.
Installation Process for Crown Plastics DuraSurf™ STS on Chute
When working with products that are pressure sensitive in nature, proper surface preparation is imperative. We always recommend that the substrate first be cleaned with an aggressive solvent-type cleaner (ex. MEK, MEK substitute, acetone).
A lacquer thinner could be used in some instances, but we recommend the aforementioned products.
Before using the solvent cleaners, use a blower to remove dust and dirt particles from the chute surface. Pay special attention to the seams and along the sides where particles can lodge and remain hidden. Using a blower will help speed the cleaning and preparation process!
Wearing latex gloves, liberally apply the cleaner to a wiping cloth and thoroughly wipe down the chute. Turn the cloth frequently to avoid recontamination. If the chute is severely contaminated, a second solvent wipe may be needed.
Once the solvent wipe is complete, perform a secondary wipe using isopropyl or denatured alcohol to remove any residue.
Make reference marks.
Based on the distance from the edge of the chute to the width of the DuraSurf™ piece being installed, use a permanent marker (suitable for metal surfaces) and a tape measure to make reference marks down the length of the chute. The reference marks should be made about every 24 inches. These will be used to keep the piece lined up properly.
Applying the DuraSurf™ STS.
Once the reference marks are in place, take a piece of the DuraSurf™ STS material and lay the entire piece down the length of the chute. Line the product up with the reference points. Leave the leading edge of the STS material about 1” from the leading edge of the chute. Doing your best to refrain from touching the adhesive with your fingers, remove the release liner from the first 6” or so of the STS material and press in place. Begin removing 12” – 24” of release liner, line up to reference marks and press in place. Work the material down, moving side-to-side to prevent air from getting trapped underneath. Continue this process down the entire length of the chute. Repeat the process for all additional strips.
Use a Roller.
Once all of the strips are in place, it is important that mechanical pressure be applied. Remember, these are PRESSURE SENSITIVE adhesive systems. They bond more effectively with mechanical pressure. Using a roller will double the bond strength to the substrate.
Crown Plastics recommends using an extension wall roller (Crain #333 or equivalent). Thoroughly apply pressure on all strips. Pay additional attention to leading edges and seams where a potential catch point may occur.
Crown Plastics recommends Avery Dennison’s HPA1905 high-performance acrylic adhesive for most material handling applications. The HPA1905’s initial bond is very good and the bond significantly increases over the first 24 hours.
A rubber adhesive can also be used. Rubber adhesives are more aggressive, but the bond is maximized immediately upon application. Rubber adhesives are also more sensitive to environmental extremes. This includes elevated temperatures, moisture and chemicals.
Where rubber adhesives have been applied, and there is concern of potential delamination at the leading edges, pop rivets can be applied as an insurance policy.
Removing and Replacing DuraSurf ™ STS UHMW-PE
When removing DuraSurf™ UHMW tapes, pry up one corner with a screwdriver or scraper and peel the plastic strip away with vice grips. Remove residual adhesive using a clean rag and lacquer thinner (or other permissible solvent). Do not use mineral spirits, as it is oil-based and will leave a film residue.
When removing the adhesive it may be necessary to scrape the residue in order to break through the carrier. The remaining adhesive can be removed by wiping with a rag and solvent. Make sure the surface is clean and dry before applying new UHMW.
DuraSurf ™ STS
DuraSurf™ STS UHMW-PE is a revolutionary product in that it possesses a Silicone Treated Surface with an adhesive backing for easy installation. The very low coefficient of friction provides a lubricated surface that is virtually maintenance free. DuraSurf™ STS is an ideal solution for many applications in the package handling industry including slider beds, slides, chute linings, spirals and any areas where packages can get lodged or damaged. DuraSurf™ STS reduces jamming and keeps packages moving smoothly to their ultimate destination. DuraSurf™ STS is also static dissipative, preventing static shocks and potential damage to bar coding systems.
DuraSurf™ STS is uniquely available with an adhesive backing to provide easy installation and eliminate the need for mechanical fastening. Die cutting is also available for washers, bushings, wear pads and anti-friction surfaces.